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December 07, 2009 — Ottawa, Ontario

They already light up Christmas trees, traffic signals, crosswalks and vehicle brakes. And they may someday completely displace incandescent lighting from the marketplace. This is because light-emitting diodes (LEDs) are at least four times more energy efficient than standard incandescent bulbs and about 25-50 times longer-lasting; other solid state lighting, such as flat panel organic LEDs (OLEDs) are not far behind.

NRC-IRC's lighting group is working with an industry consortium to study the potential applications of LEDs and OLEDs in office environments — possibly the single most important commercial lighting market. "Cost is the biggest barrier," says Dr. Newsham. "This market is currently dominated by fluorescent lighting, which is just as efficient as white LEDs and much cheaper. However, the U.S. Department of Energy predicts that LED prices will eventually come down substantially and their efficiency will practically double."

"Although it may be a while before solid-state lighting competes with fluorescent lighting on a cost-benefit basis," he adds, "this gives us an opportunity to start identifying office applications where they could provide extra value for occupants that fluorescents can't."

Customize your colours

For example, unlike fluorescent lighting, it's easy to control the colour emitted by LEDs. And, LEDs and OLEDs come in more flexible forms than standard fluorescent tubes. "This means you could use solid-state lighting in creative ways," says Dr. Newsham. "An office ceiling could glow and change colour as the outside sky goes from blue to sunset. A cubicle could change colour if an email arrives. Or, if there's a fire, all of the cubicles on the evacuation route could turn red to guide people toward the exit." He and his colleagues will explore whether such functionality is beneficial for occupants.

So far, the NRC-IRC team has completed an LED colour preference experiment, which involved a detailed one-sixth scale model of an office. "The participants were allowed to choose any mix of red, green, blue, warm white or cool white to see if there's any variation in the lighting colours that people prefer," explains Dr. Erhan Dikel, who designed the model. "We also exposed them to a set of fixed spectra to see how they would react. People generally want a shade of white, but do they want a bluer, redder or yellower white? LEDs would allow individuals to select their own preference."

"In future, we may study whether a person's ability to choose a preferred lighting colour has a measurable effect on their well-being or task performance over a full day of exposure," says Dr. Newsham. "We might also explore whether varying the spectrum throughout the day using LEDs can improve the health of office workers, a potential mechanism suggested by early explorations into the effect of light on human physiology."